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[91.12.99.11]) by smtp.gmail.com with ESMTPSA id h25sm9508172wmp.33.2021.08.05.10.29.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Aug 2021 10:29:23 -0700 (PDT) Subject: Re: [PATCH v7 1/2] mm: introduce process_mrelease system call To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: mhocko@kernel.org, mhocko@suse.com, rientjes@google.com, willy@infradead.org, hannes@cmpxchg.org, guro@fb.com, riel@surriel.com, minchan@kernel.org, christian@brauner.io, hch@infradead.org, oleg@redhat.com, jannh@google.com, shakeelb@google.com, luto@kernel.org, christian.brauner@ubuntu.com, fweimer@redhat.com, jengelh@inai.de, timmurray@google.com, linux-api@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com References: <20210805170859.2389276-1-surenb@google.com> From: David Hildenbrand Organization: Red Hat Message-ID: <46998d10-d0ca-aeeb-8dcd-41b8130fb756@redhat.com> Date: Thu, 5 Aug 2021 19:29:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210805170859.2389276-1-surenb@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.08.21 19:08, Suren Baghdasaryan wrote: > In modern systems it's not unusual to have a system component monitoring > memory conditions of the system and tasked with keeping system memory > pressure under control. One way to accomplish that is to kill > non-essential processes to free up memory for more important ones. > Examples of this are Facebook's OOM killer daemon called oomd and > Android's low memory killer daemon called lmkd. > For such system component it's important to be able to free memory > quickly and efficiently. Unfortunately the time process takes to free > up its memory after receiving a SIGKILL might vary based on the state > of the process (uninterruptible sleep), size and OPP level of the core > the process is running. A mechanism to free resources of the target > process in a more predictable way would improve system's ability to > control its memory pressure. > Introduce process_mrelease system call that releases memory of a dying > process from the context of the caller. This way the memory is freed in > a more controllable way with CPU affinity and priority of the caller. > The workload of freeing the memory will also be charged to the caller. > The operation is allowed only on a dying process. > > After previous discussions [1, 2, 3] the decision was made [4] to introduce > a dedicated system call to cover this use case. > > The API is as follows, > > int process_mrelease(int pidfd, unsigned int flags); > > DESCRIPTION > The process_mrelease() system call is used to free the memory of > an exiting process. > > The pidfd selects the process referred to by the PID file > descriptor. > (See pidfd_open(2) for further information) > > The flags argument is reserved for future use; currently, this > argument must be specified as 0. > > RETURN VALUE > On success, process_mrelease() returns 0. On error, -1 is > returned and errno is set to indicate the error. > > ERRORS > EBADF pidfd is not a valid PID file descriptor. > > EAGAIN Failed to release part of the address space. > > EINTR The call was interrupted by a signal; see signal(7). > > EINVAL flags is not 0. > > EINVAL The memory of the task cannot be released because the > process is not exiting, the address space is shared > with another live process or there is a core dump in > progress. > > ENOSYS This system call is not supported, for example, without > MMU support built into Linux. > > ESRCH The target process does not exist (i.e., it has terminated > and been waited on). > > [1] https://lore.kernel.org/lkml/20190411014353.113252-3-surenb@google.com/ > [2] https://lore.kernel.org/linux-api/20201113173448.1863419-1-surenb@google.com/ > [3] https://lore.kernel.org/linux-api/20201124053943.1684874-3-surenb@google.com/ > [4] https://lore.kernel.org/linux-api/20201223075712.GA4719@lst.de/ > > Signed-off-by: Suren Baghdasaryan > --- > changes in v7: > - Fixed pidfd_open misspelling, per Andrew Morton > - Fixed wrong task pinning after find_lock_task_mm() issue, per Michal Hocko > - Moved MMF_OOM_SKIP check before task_will_free_mem(), per Michal Hocko > > mm/oom_kill.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 73 insertions(+) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index c729a4c4a1ac..a4d917b43c73 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -28,6 +28,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -1141,3 +1142,75 @@ void pagefault_out_of_memory(void) > out_of_memory(&oc); > mutex_unlock(&oom_lock); > } > + > +SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) > +{ > +#ifdef CONFIG_MMU > + struct mm_struct *mm = NULL; > + struct task_struct *task; > + struct task_struct *p; > + unsigned int f_flags; > + struct pid *pid; > + long ret = 0; > + > + if (flags) > + return -EINVAL; > + > + pid = pidfd_get_pid(pidfd, &f_flags); > + if (IS_ERR(pid)) > + return PTR_ERR(pid); > + > + task = get_pid_task(pid, PIDTYPE_PID); > + if (!task) { > + ret = -ESRCH; > + goto put_pid; > + } > + > + /* > + * If the task is dying and in the process of releasing its memory > + * then get its mm. > + */ > + p = find_lock_task_mm(task); > + if (!p) { > + ret = -ESRCH; > + goto put_pid; > + } > + if (task != p) { > + get_task_struct(p); Wouldn't we want to obtain the mm from p ? I thought that was the whole exercise of going via find_lock_task_mm(). -- Thanks, David / dhildenb